Among Philo's attacks on empirical theism, the most famous and the most trenchant is the attack from the problem of evil. In its traditional form the problem of evil is seen as a challenge to the common conception of God. Given that there is evil in the world, the line of reasoning goes, what are we to conclude about God? Either he wishes to prevent evil and cannot, in which case he is not infinitely powerful; or else, he could prevent evil, but does not want to, in which case he may not be infinitely good; or, finally, perhaps he simply does not know the best way to run the world, in which case he is not infinitely wise. Theists want to maintain that God is infinitely powerful, good, and wise, and so the problem of evil poses a severe challenge to them.

Hume is not particularly concerned with this strong version of the problem of evil. Philo tells us that so long as we admit that God is incomprehensible there is no problem here at all: we must simply allow that while God's infinite perfection can, in fact, be reconciled with the presence of evil in the world, we have no idea how this reconciliation might occur. The only time the problem of evil really becomes a problem, he asserts, is when we try to claim that God is very strongly analogous to a human being. If God is anything like a human being, and can be judged by human standards of justice, kindness, and compassion, then he cannot be all good. In this sense, the traditional version of the problem of evil presents a real problem for the empirical theist insofar as the empirical theist believes in an anthropomorphized (i.e. human-like) God.

Hume's real concern with the problem of evil, however, is slightly different from this traditional concern about reconciliation. He is not so interested in the problem as a challenge to the traditional conception of God, as he is in the problem as a block to any inferences that we could make about God's moral nature. Given how much evil there is in our world, he argues, we cannot look at our universe and reasonably infer from the evidence that God is infinitely wise, good, and powerful. In fact, we cannot even reasonably conclude from the evidence that God is moderately good, wise, and powerful. If we were to try to draw any conclusions about God's nature just from the evidence afforded us by nature (which Philo does not believe we should do) the only warranted conclusion would be that God is indifferent between good and evil—that he is morally neutral. The argument from design then, as well as any other sort of argument for empirical theism, cannot possibly work as an argument that tells us about God's moral nature (and since God's moral nature is a pretty fundamental part of God, this weakness makes empirical theism seem pretty hopeless).

Popular pages: Dialogues Concerning Natural Religion